In the art of injecting a plastics material into a mold cavity to form a molded plastics article or part such as, for example, a control knob or a pump housing or an enclosure cabinet, it is common to provide the part with one or more threaded holes for receiving a threaded fastener which connects the part to another article or part. When it is necessary to provide the threaded hole with internal threads having substantial strength and capable of withstanding substantial axial and torsional forces, a metal insert is commonly positioned within the mold cavity on a support stud or pin prior to injecting the plastics material. When the molded plastics part is removed from the mold cavity, the metal insert remains with the molded part and provides a threaded hole for receiving a threaded connector or fastener.
Usually, the metal insert is formed or machined from solid bar stock on an automatic screw machine, for example, as disclosed in U.S. Pat. No. 1,919,455. The machine automatically drills and taps a hole within one end of the bar stock and also roughens or knurles the outer surface of the bar stock after which the bar stock is automatically cut off to form a metal insert of predetermined length. The roughened or knurled outer surface of the insert receives the injected plastics material and forms a positive connection of the insert with the molded part of plastics material. When the molded part is used in a high moisture or corrosive environment, it is desirable for the metal insert to be machined from a non-corrosive material such as aluminum, brass or stainless steel. Such a material and the machining operation significantly increase the cost of the metal insert and thereby result in increasing the cost of the molded plastic article or part.